Process for the preparation of a mineral filler product

ABSTRACT

A process for the preparation of a mineral filler product is disclosed, the process comprising a step of dry grinding a calcium carbonate-containing material in a mixture obtained by contacting the calcium carbonate-containing material with at least one grinding agent selected from specific styrene-maleic anhydride co-polymers and/or specific derivatives of styrene-maleic anhydride co-polymers.

CROSS-REFERENCE TO RELATED APPLICATIONS

This is a U.S. national phase of PCT Application No. PCT/EP2015/053000,filed Feb. 12, 2015, which claims priority to European Application No.14156165.4, filed Feb. 21, 2014.

The present invention relates to a mineral filler product which may beused in a multitude of applications, for example in polymercompositions, in paper making, paper coatings, agriculturalapplications, paints, adhesives, sealants, construction applications, orcosmetic applications.

Well-known mineral fillers comprise, for example, natural ground calciumcarbonate (GCC) and precipitated calcium carbonate (PCC).

For the preparation of GCC it has been quite common to use polymers suchas polyalkylene glycols or polymers based on partially or totallyneutralized polyacrylic acids, polymethacrylic acids, their derivativesand salts thereof, as grinding aids and dispersing agents in a grindingprocess to provide aqueous mineral suspensions.

In EP 2 029 677, a process for dry grinding a material containing acarbonate ore is described, said process includes the steps of drygrinding said material in at least one grinding unit in the presence ofat least one polyalkylene glycol polymer in such manner that thequantity of water in the grinding unit is less than 10 wt.-%, based onthe dry material in said grinding unit. The process may further comprisean optional classifying step, wherein both the grinding step and thelatter classifying step may be carried out repeatedly with all or partof the material obtained in the dry grinding step and/or in theclassifying step.

EP 2 132 268 provides a method for dry grinding of one or more mineralmaterials which include at least one calcium carbonate. The methodincludes the steps of crushing the mineral material(s) in at least onecrushing unit, dry grinding the crushed material in at least onegrinding unit in the presence of a comb-type hydrophilic polymercontaining at least one polyalkylene oxide, wherein the quantity ofliquid in the grinding unit is less than 15 wt.-%, based on the drymaterial crushed in said crushing unit. The process may further comprisean optional classifying step, wherein both the grinding step and thelatter classifying step may be carried out repeatedly with all or partof the material obtained in the dry grinding step and/or in theclassifying step.

WO 2011/077232 relates to the use of formulations containing glyceroland/or polyglycerols as an agent during dry grinding to improve theself-dispersing properties of said mineral material in an aqueouscomposition. The viscosity of the final composition is thus reduced andkept stable over time. Furthermore, the amount of foam formed during thedispersing step is reduced.

Attempts have also been made to improve the applicability of particulatemineral materials and especially calcium carbonate-containing mineralfillers, e.g., by treating such materials with higher aliphaticcarboxylic acids, which in some cases may also be referred to as fattyacids, and aliphatic carboxylic acid salts. For instance, WO 00/20336relates to an ultrafine natural calcium carbonate which may optionallybe treated with one or more several fatty acids or one or more severalsalts, or mixtures thereof, and which is used as a rheology regulatorfor polymer compositions.

Likewise, U.S. Pat. No. 4,407,986 relates to a precipitated calciumcarbonate that is surface-treated with a dispersant that may includehigher aliphatic acids and their metal salts in order to limit theaddition of lubricant additives when kneading this calcium carbonatewith crystalline polypropylene and to avoid the formation of calciumcarbonate aggregates that limit the impact strength of thepolypropylene.

In EP 0 325 114 relating to non-sagging underseal compositions for motorvehicles based on polyvinyl chloride which has improved rheological andadhesion properties, a mixture of an ammonium salt of 12-hydroxystearicacid in combination with a fatty acid (in a weight ratio of 1:1) is usedto treat a mineral filler.

Moreover, particulate mineral materials may also be treated with othersurface-treatment agents, such as silanes, siloxanes, phosphates,phosphonates, oxalates, succinates, fluorides, natural or syntheticpolymers, or mixtures thereof in order to hydrophobize the surface ofsaid mineral material.

However, in many cases, the preparation of calcium carbonate-containingmineral filler products by use of the aforementioned grinding agents anddispersants leads to a poor quality. For example, the use of grindingagents often results in a high water pick up susceptibility of theresulting mineral filler product. Particulate calciumcarbonate-containing materials having high moisture pick upsusceptibilities may also be disadvantageous when used as filler inpolymer compositions. For example, such materials may pick up moistureduring storage, transportation, and/or processing which, in turn, maylead to the formation of voids in polymer compositions produced in amelt extrusion process.

Although related to a wet grinding process, EP 0 998 522 disclosessuspensions being ground in the absence of dispersant or in presence ofonly sub-efficient amounts, which are then dried and used as a filler inpolymer products. As a general rule, the prior art teaches to useneither any dispersant nor grinding agent for the either dry or wetgrinding of calcium carbonate if intended for the use as a filler inpolymer products.

In view of the foregoing, the expert is still faced with the problem ofefficient production of dry ground fillers for the application inplastics, such as polyolefins, without a decrease in quality. Stilltoday, dry grinding processes have several disadvantages. For example,the absence of grinding agents and dispersants results in a lowthroughput and low grinding efficiency which, in turn, leads to anoverall increase in energy consumption.

There is still a need to provide mineral filler products and processesfor their preparation which may reduce or avoid one or more of theaforementioned technical drawbacks.

It is thus an object of the present invention to provide a process forthe preparation of a mineral filler product which may be carried underhigh throughput and high grinding efficiency. Another object may also beseen in the provision of a more efficient process for the provision of amineral filler product having a relatively low moisture pick upsusceptibility.

One or more of the foregoing and other problems are solved by thesubject-matter as defined herein in the independent claims.

A first aspect of the present invention relates to a process for thepreparation of a mineral filler product, said process comprising thesteps of:

-   -   a) providing a calcium carbonate-containing material;    -   b) providing at least one grinding agent;    -   c) dry grinding the calcium carbonate-containing material in a        mixture obtained by contacting:        -   i) the calcium carbonate-containing material provided in            step a), with        -   ii) the at least one grinding agent provided in step b) in            at least one grinding unit to obtain a dry ground mineral            filler;    -   d) classifying the dry ground mineral filler of step c) to        obtain a coarse fraction and a fine fraction, wherein the coarse        fraction is removed or subjected to dry grinding step c) and the        fine fraction represents a fine mineral filler; and    -   e) optionally drying the fine mineral filler of step d) to        obtain a dried mineral filler having a total moisture content of        less than 1.0 wt.-%, based on the total weight of said dried        mineral filler;    -   wherein the total moisture content in the mixture of step c) is        less than or equal to 10.0 wt.-%, based on the total weight of        said mixture;    -   the amount of the at least one grinding agent provided in        step b) ranges from 0.05 to 150 mg/m², based on the specific        surface area of the calcium carbonate-containing material as        measured by the BET nitrogen method;    -   the temperature in step c) ranges from 65° C. to 200° C.; and    -   the at least one grinding agent is selected from the group        consisting of styrene-maleic anhydride co-polymers and        derivatives of styrene-maleic anhydride co-polymers, and has a        monomer unit ratio (styrene units:maleic anhydride units, S:MA)        of from 1:2 to 15:1 and a molecular weight M_(w) of from 500 to        40,000 g/mol.

According to the process of the present invention, the mineral fillerproduct can be prepared from a calcium carbonate-containing material,for example from marble, limestone, chalk, dolomite, and the like, in adry grinding process. The present invention makes use of at least onegrinding agent selected from the group of styrene-maleic anhydrideco-polymers and derivatives of styrene-maleic anhydride co-polymersinstead of conventional agents, such as mono- or polyalkylene glycols orpolyacrylates. For this purpose, a calcium carbonate-containing materialis provided and subjected to a dry grinding step in a grinding unit(e.g., a ball mill) at elevated temperatures ranging from 65° C. to 200°C. The grinding agent may be contacted with said calciumcarbonate-containing material prior to the grinding step or during drygrinding. Upon addition of the grinding agent and during the grindingstep, a layer may be formed on at least part of the surface of the dryground mineral filler. Said layer may comprise the styrene-maleicanhydride co-polymers or derivatives of styrene-maleic anhydrideco-polymers. It may also comprise the corresponding reaction products ofthe grinding agent(s) which may result from the reaction of saidagent(s), for example, with the calcium carbonate-containing material.Typically, said reaction products are reaction products resulting fromthe reaction of the grinding agent(s) with the surface of the calciumcarbonate-containing material. Subsequently to the grinding step, thedry ground mineral filler is subjected to a classifying step. In saidclassifying step, the dry ground mineral filler is divided into a coarsefraction and a fine fraction. Whereas the fine fraction represents thefinal product which, optionally, may be subjected to a drying step toremove at least part of the moisture (i.e. water) in order to obtain adried mineral filler having a moisture content of less than 1.0 wt.-%,the coarse fraction may be removed or may be recycled by subjecting sameagain to dry grinding step c). In order to achieve optimal grindingefficiency and optimal quality of the obtainable mineral filler product,the at least one grinding agent has a monomer unit ratio (styreneunits:maleic anhydride units, S:MA) of from 1:2 to 15:1 and a molecularweight M_(w) of from 500 to 40,000 g/mol.

Another aspect of the present invention relates to a mineral fillerproduct. Said product is obtainable by the process according to thepresent invention.

Still another aspect of the present invention relates to the use of theinventive mineral filler product in a polymer composition, in papermaking, paper coatings, agricultural applications, paints, adhesives,sealants, construction applications, and/or cosmetic applications.

Advantageous embodiments of the process according to the presentinvention and embodiments of the mineral filler product obtainable bythe process according to the present invention are defined in thecorresponding subclaims.

According to one embodiment, the calcium carbonate-containing materialprovided in step a) is selected from natural calcium carbonate sourcesand preferably is selected from the group consisting of marble,limestone, chalk, dolomite, and mixtures thereof.

According to another embodiment, the amount of said at least onegrinding agent provided in step b) ranges from 0.01 to 10.0 wt.-%,preferably from 0.05 to 5.0 wt.-%, more preferably from 0.1 to 3.0wt.-%, and most preferably from 0.15 to 2.0 wt.-%, based on the totaldry weight of the calcium carbonate-containing material.

According to another embodiment, the at least one grinding agentprovided in step b) has a monomer unit ratio (S:MA) of from 1:1 to 5:1,preferably from 1:1 to 4:1, and more preferably from 1:1 to 3:1.

According to another embodiment, the at least one grinding agentprovided in step b) has a molecular weight M_(w) of from 2,000 to 30,000g/mol and preferably from 3,000 to 25,000 g/mol.

According to still another embodiment, the at least one grinding agentprovided in step b) is partially or fully neutralized with cationsselected from lithium, sodium, potassium, calcium, magnesium, ammonium,iminium, and mixtures thereof.

According to another embodiment, the total moisture content in themixture of step c) is less than or equal to 5.0 wt.-%, preferably lessthan or equal to 2.0 wt.-%, and more preferably less than or equal to1.0 wt.-%, based on the total weight of said mixture.

According to still another embodiment, the temperature in step c) rangesfrom 70° C. to 180° C., preferably from 75° C. to 160° C., and morepreferably from 80° C. to 150° C.

According to still another embodiment, the fine mineral filler of stepd) has a weight median particle size d₅₀ ranging from 0.4 to 40.0 μm,preferably from 0.6 to 20.0 μm, and more preferably from 0.7 to 10.0 μm.

According to another embodiment, the process comprises a further step oftreating the fine mineral filler of step d) and/or the dried mineralfiller of step e) with a hydrophobizing agent to obtain asurface-treated product having a treatment layer on at least part of thesurface of said product.

According to another embodiment, the product obtainable after treatingthe fine mineral filler of step d) and/or the dried mineral filler ofstep e) has a moisture pick up susceptibility of less than or equal to0.9 mg/g, preferably less than or equal to 0.8 mg/g, more preferablyless than or equal to 0.7 mg/g, and most preferably from 0.2 to 0.6mg/g.

According to another embodiment, said product has a volatile onsettemperature of at least or equal to 200° C., preferably at least orequal to 230° C., and more preferably at least or equal to 250° C.

According to another embodiment, the mineral filler product is used in apolymer composition, said polymer composition comprises:

-   -   a) at least one polymeric resin; and    -   b) from 0.1 to 90.0 wt.-%, preferably from 1.0 to 85.0 wt.-%,        and more preferably from 2.0 to 45.0 wt.-%, based on the total        weight of said polymer composition, of the mineral filler        product obtainable by the process according to the present        invention.

It should be understood that for the purposes of the present invention,the following terms have the following meanings:

The term “filler” in the meaning of the present invention refers tosubstances which may be added to materials, such as polymers,elastomers, paints, or adhesives, e.g. to lower the consumption of moreexpensive materials or to improve material or mechanical properties ofthe resulting products. The person skilled in the art very well knowsthe fillers, typically mineral fillers, used in the respective field.

The term “dry ground” or “dry grinding” in the meaning of the presentinvention refers to the comminution of a solid material by using a mill(e.g., by means of a ball mill), wherein said material to be ground hasa total moisture content of less than or equal to 10 wt.-%, based on thetotal weight of said material.

The terms “coarse” and “fine” as used herein describe the particle sizeof two fractions of a particulate material relative to each other and,thus, do not imply a specific particle size or size range. Unlessindicated otherwise, both terms refer to the relative weight medianparticle sizes d₅₀. In this respect, the term “fine fraction” indicatesthat the weight median particle size d₅₀ of said fraction is smallerthan the weight median particle size d₅₀ of the corresponding “coarsefraction”.

Unless specified otherwise, the terms “drying” refers to a processaccording to which at least a portion of water is removed from amaterial to be dried such that a constant weight of the obtained “dried”material at 120° C. is reached. Moreover, a “dried” material may befurther defined by its total moisture content which, unless specifiedotherwise, is less than or equal to 1.0 wt.-%, preferably less than orequal to 0.5 wt.-%, more preferably less than or equal to 0.2 wt.-%, andmost preferably between 0.03 and 0.07 wt.-%, based on the total weightof the dried material.

The “total moisture content” of a material refers to the percentage ofmoisture (i.e. water) which may be desorbed from a sample upon heatingto 220° C.

A “natural calcium carbonate source” may be any natural materialcomprising calcium carbonate. Such materials comprise, for example,marble, limestone, chalk, dolomite, and the like.

The “moisture pick up susceptibility” of a material refers to the amountof moisture absorbed on the surface of said material within a certaintime upon exposure to a defined humid atmosphere and is expressed inmg/g. The “normalized moisture pick up susceptibility” of a materialrefers to the amount of moisture absorbed on the surface of saidmaterial within a certain time upon exposure to a defined humidatmosphere and is expressed in mg/m².

The term “volatile onset temperature” the meaning of the presentapplication refers to a temperature at which volatiles—includingvolatiles introduced as a result of the present process—begin to evolve,as observed on a thermogravimetric (TGA) curve, plotting the mass ofremaining sample (y-axis) as a function of temperature (x-axis), thepreparation and interpretation of such a curve being defined hereafterin the experimental part.

Throughout the present application, the particle size of a fraction of aparticulate material is described by its particle size distribution. Thevalue d_(x) represents the diameter relative to which x % by weight ofthe particles have diameters less than d_(x). This means, for example,that the d₉₈ value (also referred to as the “topcut”) is the particlesize at which 98 wt.-% of all particles of a fraction are smaller thanthe indicated value. The d₅₀ value is thus the “weight median particlesize” at which 50 wt.-% of all particles are smaller than the indicatedparticle size.

Unless stated otherwise, the “molecular weight” or “M_(w)” of a polymeras used herein refers to the weight average molecular weight as measuredaccording to the method described hereinafter.

Where an indefinite or definite article is used when referring to asingular noun, e.g., “a”, “an” or “the”, this includes a plural of thatnoun unless anything else is specifically stated.

Where the term “comprising” is used in the present description andclaims, it does not exclude other elements. For the purposes of thepresent invention, the term “consisting of” is considered to be apreferred embodiment of the term “comprising”. If hereinafter a group isdefined to comprise at least a certain number of embodiments, this isalso to be understood to disclose a group, which preferably consistsonly of these embodiments.

Terms like “obtainable” or “definable” and “obtained” or “defined” areused interchangeably. This, e.g., means that, unless the context clearlydictates otherwise, the term “obtained” does not mean to indicate that,e.g., an embodiment must be obtained by, e.g., the sequence of stepsfollowing the term “obtained” though such a limited understanding isalways included by the terms “obtained” or “defined” as a preferredembodiment.

According to the process of the present invention, a mineral fillerproduct may be prepared from a calcium carbonate-containing material.Said process comprises a dry grinding step which is carried out in thepresence of at least one grinding agent selected from styrene-maleicanhydride co-polymers and derivatives of styrene-maleic anhydrideco-polymers. The presence of said at least one grinding agent during drygrinding leads to a dry ground mineral filler which may provide a layeron at least a part of the surface of the dry ground mineral filler,wherein said layer may comprise said at least one grinding agent. Aswill be discussed herein later in more detail, the presence of said atleast one grinding agent during the dry grinding step may also lead tothe formation of reaction products resulting from the reaction of thecalcium carbonate-containing material provided in step a) with said atleast one grinding agent provided in step b). Said reaction product mayalso form part of the layer being present on at least a part of thesurface of the dry ground mineral filler.

The inventors surprisingly found that the mineral filler productobtainable by the process according to the present invention providesseveral advantages. For example, the at least one styrene-maleicanhydride co-polymer and/or at least one derivative of a styrene-maleicanhydride co-polymer may be used as a substitute for conventionalgrinding agents and dispersing agents, such as mono- or polyalkyleneglycols or polyacrylates.

The problems described hereinabove with respect to the prior art may besolved by the process according to the present invention using efficientamounts of specific styrene-maleic anhydride co-polymers or derivativesthereof. The use of the grinding agents as described herein may resultin higher mill capacities and a higher throughput. In turn, lowerinvestments and smaller plant footprints for equal production capacitiesare required.

In the following, preferred embodiments of the process according to thepresent invention for the preparation of a mineral filler product willbe discussed in more detail. It is to be understood that these detailsand embodiments also apply to the mineral filler product itself as wellas to the use of said product in any of the disclosed applications.

Process Step a)

According to step a) of the process according to the present invention,a calcium carbonate-containing material is provided. In general, saidcalcium carbonate-containing material may be any calcium carbonatesource and may be of natural or synthetic origin.

In some embodiments of the process according to the present invention,the calcium carbonate-containing material provided in step a) isselected from natural calcium carbonate sources, preferably containingfrom 50 to 98 wt.-% of calcium carbonate, based on the total weight ofsaid calcium carbonate-containing material.

According to one embodiment, the calcium carbonate-containing materialcontains at least 50 wt.-%, preferably at least 70 wt.-%, morepreferably at least 80 wt.-%, even more preferably at least 90 wt.-%,and most preferably from 90 to 98 wt.-% of calcium carbonate, based onthe total weight of said calcium carbonate-containing material.

According to another embodiment, the calcium carbonate-containingmaterial provided in step a) is selected from the group consisting ofmarble, limestone, chalk, dolomite, and mixtures thereof.

According to a preferred embodiment, the calcium carbonate-containingmaterial provided in step a) is selected from the group consisting ofmarble, limestone, chalk, and mixtures thereof.

In cases where the calcium carbonate is of synthetic origin, the calciumcarbonate-containing may be precipitated calcium carbonate (PCC). A PCCin the meaning of the present invention is a synthesized material,generally obtained by precipitation following a reaction of carbondioxide and calcium hydroxide (hydrated lime) in an aqueous environmentor by precipitation of a calcium- and a carbonate source in water.Additionally, precipitated calcium carbonate can also be the product ofintroducing calcium and carbonate salts, calcium chloride and sodiumcarbonate, for example, in an aqueous environment. PCC may be vaterite,calcite or aragonite. PCCs are described, for example, in EP 2 447 213,EP 2 524 898, EP 2 371 766, or unpublished European patent applicationNo. 12 164 041.1.

Suitably, the calcium carbonate-containing material of step a) isprovided as a solid material being in particulate form. In this respect,the calcium carbonate-containing material provided in step a) may haveany particle size distribution allowing the material to be subjected toa dry grinding step. Therefore, the calcium carbonate-containingmaterial may be provided as a comminuted material, for example, incrushed or preground form.

According to one embodiment, the calcium carbonate-containing materialprovided in step a) has a weight median particle size d₅₀ ranging from5.0 to 600.0 μm and preferably from 50.0 to 300.0 μm.

Process Step b)

According to step b) of the process according to the present invention,at least one grinding agent is provided. A “grinding agent” in themeaning of the present invention may be any compound which may be addedprior to and/or during a grinding step (e.g., dry grinding) in order toenhance the grinding performance.

The inventors surprisingly found that it is of particular advantage touse at least one grinding agent selected from the group consisting ofstyrene-maleic anhydride co-polymers and derivatives of styrene-maleicanhydride co-polymers, wherein said grinding agent has a monomer unitratio (styrene units:maleic anhydride units, S:MA) of from 1:2 to 15:1and a molecular weight M_(w) of from 500 to 40,000 g/mol.

For the purpose of the present invention, styrene-maleic anhydrideco-polymers (SMAs) may be defined by their “monomer unit ratio” of thepolymer chain, i.e. by the monomer unit ratio (S:MA) of styrene units(S) to maleic anhydride (MA) units.

Unless indicated otherwise, the ratio (S:MA) is used likewise to definethe monomer unit ratio of:

-   -   derivatives of styrene-maleic anhydride co-polymers (SMA        derivatives);    -   reaction products of styrene-maleic anhydride co-polymers        (reaction products of SMAs); and    -   reaction products of derivates of styrene-maleic anhydride        co-polymers (reaction products of SMA derivatives).

Said reaction products typically result from the reaction of the calciumcarbonate-containing material provided in step a) with said at least onegrinding agent provided in step b).

As will become more apparent from the embodiments herein below, themonomer unit ratio (S:MA) thus, on the one hand, includes styrene units,modified styrene units (present in SMA derivatives) and reactionproducts of both and, on the other hand, includes maleic anhydrideunits, modified maleic anhydride units (present in SMA derivatives) andreaction products of both.

Styrene-maleic anhydride co-polymers in the meaning of the presentinvention may be any polymers obtainable by co-polymerizing styrene andmaleic anhydride, e.g., linear or branched random co-polymers, linear orbranched block co-polymers, or a mixture thereof.

Therefore, according to one embodiment, the at least one grinding agentis selected from virgin styrene-maleic anhydride co-polymers, i.e. fromunmodified styrene-maleic anhydride co-polymers (in the art alsoreferred to as SMA or SMAnh).

According to a preferred embodiment, the at least one grinding agent isselected from derivatives of styrene-maleic anhydride co-polymers (SMAderivatives), preferably said at least one grinding agent is selectedfrom derivatives of styrene-maleic anhydride co-polymers havingpartially or fully hydrolyzed maleic anhydride units and/or partially orfully esterified maleic anhydride units and/or partially or fullyamidized maleic anhydride units and/or partially or fully imidizedmaleic anhydride units.

Derivatives of styrene-maleic anhydride co-polymers (SMA derivatives)may be any polymers obtainable by:

-   -   a) co-polymerizing styrene and maleic anhydride to obtain        co-polymers and further subjecting said co-polymers to a        modification step; or    -   b) co-polymerizing a mixture comprising a styrene monomer and a        maleic anhydride monomer to obtain co-polymers, wherein at least        a part of one or both of the two monomers is a modified monomer        and, optionally, subjecting said co-polymers to a modification        step.

In a preferred embodiment, SMA derivatives may be any polymersobtainable by co-polymerizing styrene and maleic anhydride to obtainco-polymers and further subjecting said co-polymers to a modificationstep.

Said modification of the co-polymers typically leads to a partial orfull modification of the styrene-maleic anhydride co-polymers, i.e. tostyrene-maleic anhydride co-polymers having partially or fully modifiedmonomer units. Accordingly, the derivatives of styrene-maleic anhydrideco-polymers in the meaning of the present invention may have partiallyor fully modified styrene units and/or partially or fully modifiedmaleic anhydride units, preferably partially modified styrene unitsand/or partially modified maleic anhydride units, and more preferablyfully modified styrene units and/or fully modified maleic anhydrideunits.

Unless dictated otherwise, the term “partially modified” as used hereinindicates that SMA derivatives still comprise unmodified monomerunit(s), e.g., unmodified styrene units or unmodified maleic anhydrideunits. In contrast thereto, the term “fully modified” indicates that anymonomer unit present in an SMA derivative is modified, e.g., any styreneunit or any maleic anhydride unit. The same meaning also applies to morespecific modifications: In this respect, the term “partially hydrolyzedmaleic anhydride units”, for example, means that a derivative of astyrene-maleic anhydride co-polymer may still comprise non-hydrolyzedmaleic anhydride units, whereas the term “fully hydrolyzed maleicanhydride units” means that all maleic anhydride units of the SMAderivative are in a hydrolyzed form.

According to one embodiment, the derivatives of styrene-maleic anhydrideco-polymers are selected from styrene-maleic anhydride co-polymershaving partially or fully modified maleic anhydride units, preferablyhaving partially modified maleic anhydride units, and more preferablyhaving fully modified maleic anhydride units.

According to another embodiment, the derivatives of styrene-maleicanhydride co-polymers are selected from styrene-maleic anhydrideco-polymers obtainable by co-polymerizing styrene and maleic anhydrideto obtain co-polymers and further subjecting said co-polymers to amodification step, said derivatives having partially or fully modifiedmaleic anhydride units, preferably having partially modified maleicanhydride units, and more preferably having fully modified maleicanhydride units.

According to one embodiment, the modification step comprises thereaction with metal hydroxides, ammonia, amines, imines, alcohols,carboxylic acids, mineral acids, and mixtures thereof.

According to a preferred embodiment, the modification step comprises thereaction with metal hydroxides, preferably alkali metal hydroxides, andmore preferably sodium hydroxide, potassium hydroxide, and mixturesthereof.

Therefore, the derivatives of styrene-maleic anhydride co-polymers maybe selected from styrene-maleic anhydride co-polymers obtainable byco-polymerizing styrene and maleic anhydride to obtain co-polymers andfurther subjecting said co-polymers to a modification step comprisingthe reaction with metal hydroxides, ammonia, amines, imines, alcohols,carboxylic acids, mineral acids, and mixtures thereof, said derivativeshaving partially or fully modified maleic anhydride units, preferablyhaving partially modified maleic anhydride units, and more preferablyhaving fully modified maleic anhydride units.

According to another embodiment, the modification step comprises thereaction with alkali metal hydroxides, ammonia, primary amines, C1-C10alcohols, C1-C10 carboxylic acids, hydrochloric acid, phosphoric acid,sulfuric acid, and mixtures thereof.

According to another embodiment, the derivatives of styrene-maleicanhydride co-polymers thus are selected from styrene-maleic anhydrideco-polymers obtainable by co-polymerizing styrene and maleic anhydrideto obtain co-polymers and further subjecting said co-polymers to amodification step comprising the reaction with alkali metal hydroxides,ammonia, primary amines, C1-C10 alcohols, C1-C10 carboxylic acids,hydrochloric acid, phosphoric acid, sulfuric acid, and mixtures thereof,said derivatives having partially or fully modified maleic anhydrideunits, preferably having partially modified maleic anhydride units, andmore preferably having fully modified maleic anhydride units.

According to another embodiment, the derivatives of styrene-maleicanhydride co-polymers are selected from styrene-maleic anhydrideco-polymers obtainable by co-polymerizing styrene and maleic anhydrideto obtain co-polymers and further subjecting said co-polymers to amodification step comprising the reaction with sodium hydroxide,potassium hydroxide, and mixtures thereof, said derivatives havingpartially or fully modified maleic anhydride units, preferably havingpartially modified maleic anhydride units, and more preferably havingfully modified maleic anhydride units.

As disclosed hereinabove, the derivatives of styrene-maleic anhydrideco-polymers may be styrene-maleic anhydride co-polymers having partiallyor fully modified styrene units and/or partially or fully modifiedmaleic anhydride units, and preferably said SMA derivatives may bestyrene-maleic anhydride co-polymers having partially or fully modifiedmaleic anhydride units. The term “modified” as used herein indicatesthat a polymer comprises monomer units which may be obtainable frommodifications steps, for example, by the formation of hydrolysates(e.g., hydrolyzed maleic anhydride units), esters (e.g., esterifiedmaleic anhydride units), amides (e.g., amidized maleic anhydride units),and imides (e.g., imidized maleic anhydride units).

In this respect, styrene-maleic anhydride co-polymers having hydrolyzedmaleic anhydride units, for example, may comprise carboxyl groups[—C(═O)OH] and/or carboxylate groups [—C(═O)O⁻]. Accordingly,styrene-maleic anhydride co-polymers having esterified maleic anhydrideunits may comprise ester groups [—C(═O)OR] resulting from a modificationstep using alcohols, such as methanol, ethanol, and the like, whereasstyrene-maleic anhydride co-polymers having amidized maleic anhydrideunits may comprise amide moieties [—C(═O)NHR] resulting from amodification step using amines, such as ammonia, primary amines (e.g.,methylamine, dimethylaminopropylamine), and secondary amines (e.g.,dimethylamine). Imide moieties [—C(═O)NHC(═O)—] as present instyrene-maleic anhydride co-polymers having imidized maleic anhydrideunits may also result from modifications using amines such as ammonia orprimary amines (e.g., methylamine, dimethylaminopropylamine) but,however, require a nucleophilic substitution with a single amine moietyon both carbonyl groups of the maleic anhydride unit.

In general, a modification of the maleic anhydride unit—from a chemicalpoint of view—may comprise at least one modification at the firstcarbonyl group and, alternatively, another nucleophilic substitution atthe second carbonyl group of the maleic anhydride unit. In particular,this applies to styrene-maleic anhydride co-polymers having partially orfully esterified maleic anhydride units as well as to styrene-maleicanhydride co-polymers having partially or fully amidized maleicanhydride units which thus may comprise mono- and/or diester units (i.e.“monoesterified” and/or “diesterified” maleic anhydride units) as wellas mono- and diamide monomer units (i.e. “monoamidized” and/or“diamidized” maleic anhydride units).

If not indicated otherwise, the terms “esterified maleic anhydrideunits” and “amidized maleic anhydride units” encompasses both mono- anddimodified maleic anhydride units.

As already outlined above, imidized styrene-maleic anhydride co-polymersare formed by a substitution at both carbonyl groups of a maleicanhydride unit which, in turn, renders a further specificationredundant. In case of hydrolytic modifications, e.g., in a modificationstep using a metal hydroxide, a dicarboxylic acid or dicarboxylate unitis already obtained after nucleophilic substitution at the firstcarbonyl group. Consequently the term “hydrolyzed” implies the presenceof two carboxylic groups [—C(═O)OH or —C(═O)O⁻ or both] and does alsonot require any specification whether the maleic anhydride group ismonohydrolyzed or dihydrolyzed.

According to one embodiment, the derivatives of styrene-maleic anhydrideco-polymers are selected from styrene-maleic anhydride co-polymershaving partially or fully hydrolyzed maleic anhydride units and/orpartially or fully esterified maleic anhydride units and/or partially orfully amidized maleic anhydride units and/or partially or fully imidizedmaleic anhydride units.

According to one embodiment, the derivatives of styrene-maleic anhydrideco-polymers are selected from styrene-maleic anhydride co-polymershaving partially or fully hydrolyzed maleic anhydride units, preferablyhaving partially hydrolyzed maleic anhydride units, and more preferablyhaving fully hydrolyzed maleic anhydride units.

According to one embodiment, the derivatives of styrene-maleic anhydrideco-polymers are selected from styrene-maleic anhydride co-polymershaving partially or fully esterified maleic anhydride units, preferablyhaving partially esterified maleic anhydride units, and more preferablyhaving fully esterified maleic anhydride units.

According to one embodiment, the derivatives of styrene-maleic anhydrideco-polymers are selected from styrene-maleic anhydride co-polymershaving partially or fully amidized maleic anhydride units, preferablyhaving partially amidized maleic anhydride units, and more preferablyhaving fully amidized maleic anhydride units.

According to one embodiment, the derivatives of styrene-maleic anhydrideco-polymers are selected from styrene-maleic anhydride co-polymershaving partially or fully imidized maleic anhydride units, preferablyhaving partially imidized maleic anhydride units, and more preferablyhaving fully imidized maleic anhydride units.

According to a preferred embodiment, the derivatives of styrene-maleicanhydride co-polymers are selected from styrene-maleic anhydrideco-polymers having:

-   -   a) partially or fully hydrolyzed maleic anhydride units; and/or    -   b) partially or fully mono- and/or diesterified maleic anhydride        units; and/or    -   c) partially or fully mono- and/or diamidized maleic anhydride        units; and/or    -   d) partially or fully imidized maleic anhydride units.

According to another preferred embodiment, the derivatives ofstyrene-maleic anhydride co-polymers are selected from styrene-maleicanhydride co-polymers having:

-   -   a) partially hydrolyzed maleic anhydride units; and/or    -   b) partially mono- and/or diesterified maleic anhydride units;        and/or    -   c) partially mono- and/or diamidized maleic anhydride units;        and/or    -   d) partially imidized maleic anhydride units.

According to still another preferred embodiment, the derivatives ofstyrene-maleic anhydride co-polymers are selected from styrene-maleicanhydride co-polymers having:

-   -   a) fully hydrolyzed maleic anhydride units; and/or    -   b) fully mono- and/or diesterified maleic anhydride units;        and/or    -   c) fully mono- and/or diamidized maleic anhydride units; and/or    -   d) fully imidized maleic anhydride units.

According to another embodiment of the present invention, thederivatives of styrene-maleic anhydride co-polymers may be partially orfully neutralized with mono- or divalent cations selected from lithium,sodium, potassium, calcium, magnesium, ammonium, iminium, and mixturesthereof, meaning that protons present in the derivatives ofstyrene-maleic anhydride co-polymers may be partially or fully replacedby any of the aforementioned cations. Said neutralization may beachieved, for example, by adjustment to a specific pH value usingreagents such as metal hydroxides (e.g., sodium hydroxide, potassiumhydroxide), amines (e.g., ammonia, polyethylenimine), or imines. Typicalprotons that may be replaced are those found in carboxylic acids[—C(═O)OH], sulfonic acids [—S(═O)₂OH], and/or imides [—C(═O)NHC(═O)—].The skilled person knows how to partially or fully replace protons bymono- or divalent cations and also knows how to determine whether aderivative is partially or fully neutralized.

However, in cases where the derivatives of styrene-maleic anhydrideco-polymers comprise basic groups (e.g., amines), the derivatives of astyrene-maleic anhydride co-polymers may also be neutralized by theaddition of C1-C10 carboxylic acids (e.g., acetic acid), mineral acids(e.g., hydrochloric acid, phosphoric acid, or sulfuric acid), andmixtures thereof.

Accordingly, the derivatives of styrene-maleic anhydride co-polymers maybe selected from styrene-maleic anhydride co-polymers having partiallyor fully modified styrene units and/or partially or fully modifiedmaleic anhydride units, wherein said derivatives are partially or fullyneutralized with mono- or divalent cations selected from lithium,sodium, potassium, calcium, magnesium, ammonium, iminium, and mixturesthereof.

According to another embodiment, the derivatives of styrene-maleicanhydride co-polymers are selected from styrene-maleic anhydrideco-polymers having partially or fully hydrolyzed maleic anhydride unitsand/or partially or fully esterified maleic anhydride units and/orpartially or fully amidized maleic anhydride units and/or partially orfully imidized maleic anhydride units, wherein said derivatives arepartially or fully neutralized with mono- or divalent cations selectedfrom lithium, sodium, potassium, calcium, magnesium, ammonium, iminium,and mixtures thereof.

According to a preferred embodiment, the derivatives of styrene-maleicanhydride co-polymers are selected from styrene-maleic anhydrideco-polymers having:

-   -   a) partially or fully hydrolyzed maleic anhydride units; and/or    -   b) partially or fully mono- and/or diesterified maleic anhydride        units; and/or    -   c) partially or fully mono- and/or diamidized maleic anhydride        units; and/or    -   d) partially or fully imidized maleic anhydride units;        wherein said derivatives are partially or fully neutralized with        mono- or divalent cations selected from lithium, sodium,        potassium, calcium, magnesium, ammonium, iminium, and mixtures        thereof.

According to still another embodiment, the derivatives of styrene-maleicanhydride co-polymers are selected from styrene-maleic anhydrideco-polymers having partially or fully hydrolyzed maleic anhydride units,preferably having partially hydrolyzed maleic anhydride units, and morepreferably having fully hydrolyzed maleic anhydride units, wherein saidderivatives are partially or fully neutralized with mono- or divalentcations selected from lithium, sodium, potassium, calcium, magnesium,ammonium, iminium, and mixtures thereof.

According to still another embodiment, the derivatives of styrene-maleicanhydride co-polymers are selected from styrene-maleic anhydrideco-polymers having partially or fully esterified maleic anhydride units,preferably having partially esterified maleic anhydride units, and morepreferably having fully esterified maleic anhydride units, wherein saidderivatives are partially or fully neutralized with mono- or divalentcations selected from lithium, sodium, potassium, calcium, magnesium,ammonium, iminium, and mixtures thereof.

According to still another embodiment, the derivatives of styrene-maleicanhydride co-polymers are selected from styrene-maleic anhydrideco-polymers having partially or fully amidized maleic anhydride units,preferably having partially amidized maleic anhydride units, and morepreferably having fully amidized maleic anhydride units, wherein saidderivatives are partially or fully neutralized with mono- or divalentcations selected from lithium, sodium, potassium, calcium, magnesium,ammonium, iminium, and mixtures thereof.

According to still another embodiment, the derivatives of styrene-maleicanhydride co-polymers are selected from styrene-maleic anhydrideco-polymers having partially or fully imidized maleic anhydride units,preferably having partially imidized maleic anhydride units, and morepreferably having fully imidized maleic anhydride units, wherein saidderivatives are partially or fully neutralized with mono- or divalentcations selected from lithium, sodium, potassium, calcium, magnesium,ammonium, iminium, and mixtures thereof.

In another embodiment of the present invention, the derivatives ofstyrene-maleic anhydride co-polymers further comprise partially or fullymodified styrene units, preferably the partially or fully modifiedstyrene units are fully or partially sulfonated styrene units, morepreferably the partially or fully modified styrene units are partiallysulfonated styrene units, and most preferably the partially or fullymodified styrene units are fully sulfonated styrene units.

According to a preferred embodiment, the derivatives of styrene-maleicanhydride co-polymers thus are selected from styrene-maleic anhydrideco-polymers having:

-   -   a) maleic anhydride units being        -   i) partially or fully hydrolyzed; and/or        -   ii) partially or fully mono- and/or diesterified; and/or        -   iii) partially or fully mono- and/or diamidized; and/or        -   iv) partially or fully imidized;            and/or    -   b) styrene units being partially or fully sulfonated;        wherein said derivatives of styrene-maleic anhydride co-polymers        are partially or fully neutralized with mono- or divalent        cations selected from lithium, sodium, potassium, calcium,        magnesium, ammonium, iminium, and mixtures thereof.

According to another preferred embodiment, the derivatives ofstyrene-maleic anhydride co-polymers thus are selected fromstyrene-maleic anhydride co-polymers having:

-   -   a) maleic anhydride units being        -   i) partially hydrolyzed; and/or        -   ii) partially mono- and/or diesterified; and/or        -   iii) partially mono- and/or diamidized; and/or        -   iv) partially imidized;            and/or    -   b) styrene units being partially or fully sulfonated;        wherein said derivatives of styrene-maleic anhydride co-polymers        are partially or fully neutralized with mono- or divalent        cations selected from lithium, sodium, potassium, calcium,        magnesium, ammonium, iminium, and mixtures thereof.

According to still another preferred embodiment, the derivatives ofstyrene-maleic anhydride co-polymers are selected from styrene-maleicanhydride co-polymers having:

-   -   a) maleic anhydride units being        -   i) fully hydrolyzed; or        -   ii) fully mono- and/or diesterified; or        -   iii) fully mono- and/or diamidized; or        -   iv) fully imidized;            and/or    -   b) styrene units being partially or fully sulfonated;        wherein said derivatives of styrene-maleic anhydride co-polymers        are fully neutralized with mono- or divalent cations selected        from lithium, sodium, potassium, calcium, magnesium, ammonium,        iminium, and mixtures thereof.

The styrene-maleic anhydride co-polymers having partially or fullyesterified (mono- and/or diesterified) maleic anhydride units and/orpartially or fully amidized (mono- and/or diamidized) maleic anhydrideunits and/or partially or fully imidized maleic anhydride units, may besubstituted with linear, branched, aliphatic, cyclic, saturated andunsaturated organyl groups, preferably said organyl groups have a totalamount of carbon atoms from C1 to C10, more preferably from C1 to C5,and most preferably from C1 to C3.

For the purposes of the present invention, the at least one grindingagent (i.e. both the styrene-maleic anhydride co-polymers andderivatives of styrene-maleic anhydride co-polymers) provided in step b)may have a monomer unit ratio (styrene units:maleic anhydride units,S:MA) of from 1:2 to 15:1.

According to one embodiment, the at least one grinding agent provided instep b) has a monomer unit ratio (S:MA) of from 1:1 to 5:1, preferablyfrom 1:1 to 4:1, and more preferably from 1:1 to 3:1.

Additionally or alternatively, the at least one grinding agent may alsobe defined by its molecular weight M_(w) which may be in the range from500 to 40,000 g/mol.

According to another embodiment, the at least one grinding agentprovided in step b) has a molecular weight M_(w) of from 1,000 to 40,000g/mol, preferably from 2,000 to 30,000 g/mol, and more preferably from3,000 to 25,000 g/mol.

According to still another embodiment, the at least one grinding agentprovided in step b) has a molecular weight M_(w) of from 1,000 to 40,000g/mol and a monomer unit ratio (S:MA) of from 1:1 to 5:1, preferablyfrom 1:1 to 4:1, and more preferably from 1:1 to 3:1.

According to still another embodiment, the at least one grinding agentprovided in step b) has a molecular weight M_(w) of from 2,000 to 30,000g/mol and a monomer unit ratio (S:MA) of from 1:1 to 5:1, preferablyfrom 1:1 to 4:1, and more preferably from 1:1 to 3:1.

According to still another embodiment, the at least one grinding agentprovided in step b) has a molecular weight M_(w) of from 3,000 to 25,000g/mol and a monomer unit ratio (S:MA) of from 1:1 to 5:1, preferablyfrom 1:1 to 4:1, and more preferably from 1:1 to 3:1.

The at least grinding may be provided in undiluted form or in form of anaqueous solution. The undiluted form may comprise, for example, powdersor flakes, being essentially free of water.

According to one embodiment of the present invention, the at least onegrinding agent is thus provided in undiluted form, preferably containingless than or equal to 5.0 wt.-%, more preferably less than or equal to2.0 wt.-%, even more preferably less than or equal to 1.5 wt.-%, andmost preferably from 0.01 to 1.2 wt.-% of water, based on the totalweight of said at least one grinding agent.

According to a preferred embodiment, the at least one grinding agentprovided in step b) is provided in form of an aqueous solution.

In cases where the at least one grinding agent is provided as an aqueoussolution, said solution may comprise a defined amount of said at leastone grinding agent, wherein highly concentrated solutions may bepreferred in order to keep the total moisture content in the mixture ofgrinding step c) at 10.0 wt.-% or below.

According to one embodiment, the at least one grinding agent provided instep b) is provided in form of an aqueous solution comprising from 5.0to 50.0 wt.-%, preferably from 10.0 to 45.0 wt.-%, and more preferablyfrom 20.0 to 40.0 wt.-%, based on the total weight of the solution, ofsaid at least one grinding agent.

According to another embodiment, said aqueous solution has a pH valueranging from pH 4.0 to 12.0, preferably from pH 6.0 to 11.0, and morefrom pH 7.5 to 10.5.

The amount of the at least one grinding agent may be adjusted to thespecific needs. In many cases, the amount of grinding agent may be basedon the specific surface area of the carbonate-containing materialprovided in step a). According to the present invention, the amount ofsaid at least one grinding agent provided in step b) ranges from 0.05 to150 mg/m², based on the specific surface area of the calciumcarbonate-containing material as measured by the BET nitrogen method.Unless specifically stated, the amount of the at least one grindingagent is to be understood as a total amount. In cases where saidgrinding agent is added in one portion, the indicated amount thus refersto the amount of said one portion. Accordingly, in cases where thegrinding agent is added in more than one portions, the indicated amountthus refers to the total amount of said portions.

In one embodiment of the process according to the present invention, theamount of said at least one grinding agent provided in step b) rangesfrom 0.1 to 100.0 mg/m², preferably from 0.2 to 75.0 mg/m², and morepreferably from 0.2 to 50.0 mg/m², based on the specific surface area ofthe calcium carbonate-containing material as measured by the BETnitrogen method.

According to another embodiment, the amount of said at least onegrinding agent provided in step b) ranges from 0.1 to 25.0 mg/m²,preferably from 0.2 to 15.0 mg/m².

However, the amount of said at least one grinding agent provided in stepb) may also be based on the total dry weight of the calciumcarbonate-containing material provided in step a).

According to one embodiment, the amount of said at least one grindingagent provided in step b) thus ranges from 0.05 to 5.0 wt.-%, preferablyfrom 0.1 to 3.0 wt.-%, and more preferably from 0.15 to 2.0 wt.-%, basedon the total dry weight of the calcium carbonate-containing material.

According to another embodiment, the amount of said at least onegrinding agent provided in step b) ranges from 0.01 to 1.0 wt.-%,preferably from 0.05 to 0.75 wt.-%, and more preferably from 0.1 to 0.5wt.-%, based on the total dry weight of the calcium carbonate-containingmaterial.

Process Step c)

According to step c) of the process according to the present invention,a mixture obtained by contacting the calcium carbonate-containingmaterial provided in step a) with the at least one grinding agentprovided in step b) is dry ground in at least one grinding unit toobtain a dry ground mineral filler.

The term “dry ground” or “dry grinding” in the meaning of the presentinvention refers to the comminution of a solid material by using a mill(e.g., by means of a ball mill), wherein said material to be ground hasa total moisture content of less than or equal to 10 wt.-%, based on thetotal weight of said material.

For the purposes of the present invention, any suitable mill known inthe art may be used. However, said at least one grinding unit preferablyis a ball mill. It has to be noted that step c) is carried out by usingat least one grinding unit, i.e. it is also possible to use a series ofgrinding units which may, for example, be selected from ball mills,semi-autogenous mills, or autogenous mills.

The amount of water being present in the mixture to be ground may beexpressed by the total moisture content which is based on the totalweight of said mixture. Typically, dry grinding processes are carriedusing mixtures having a total moisture of less than or equal to 10.0wt.-%, based on the total weight of said mixture.

According to one embodiment, the total moisture content in the mixtureof step c) is less than or equal to 5.0 wt.-%, preferably less than orequal to 2.0 wt.-%, and more preferably less than or equal to 1.0 wt.-%,based on the total weight of said mixture.

According to another embodiment, the total moisture content in themixture of step c) is less than or equal to 5.0 wt.-%, preferably lessthan or equal to 2.0 wt.-%, and more preferably less than or equal to1.0 wt.-%, based on the total weight of said mixture, wherein the totalmoisture content in the mixture of step c) preferably has a lower limitof 0.03 wt.-%, based on the total weight of said mixture.

According to still another embodiment of the process according to thepresent invention, the total moisture content in the mixture of step c)is less than or equal to 0.2 wt.-%, preferably less than or equal to 0.1wt.-%, and more preferably between 0.03 and 0.07 wt.-%, based on thetotal weight of said mixture.

The calcium carbonate-containing material provided in step a) mayundergo reactions with said at least one grinding agent provided in stepb) upon contacting with each other said components to form a mixture.Said reaction products(s) may thus be present in the mixture of step c)but also may be present in any of the following process steps. Suchreaction products(s) may be formed on the surface of the calciumcarbonate-containing material which may result in one or more reactionproduct(s) being bound to the surface of the calciumcarbonate-containing material. However, said reaction product(s) mayalso be present in the mixture without being bound to any othercomponent present in said mixture of step c) or in any of the followingprocess steps.

Therefore, in one embodiment of the process according to the presentinvention, the mixture of step c) may be obtained by contacting:

-   -   i) the calcium carbonate-containing material provided in step        a), with    -   ii) the at least one grinding agent provided in step b),        wherein at least a part of one or both components may be present        in said mixture in form of one or more reaction products        resulting from the reaction of the calcium carbonate-containing        material provided in step a) with said at least one grinding        agent provided in step b).

According to another embodiment, said mixture of step c) comprises oneor more lithium, sodium, potassium, strontium, calcium, magnesium and/oraluminum salts of the at least one grinding agent provided in step b).

According to step c) of the process according to the present invention,a mixture obtained by contacting a calcium carbonate-containing materialwith at least one grinding agent is dry ground in at least one grindingunit to obtain a dry ground mineral filler.

In this respect, it is possible to obtain the mixture to be ground instep c) of the process according to the present invention by contactingwith each other the components provided in steps a) and b) prior to orduring grinding step c). In addition, it is also possible to obtain saidmixture by contacting with each other the components in one or moreportions prior to or during grinding.

According to one embodiment, the mixture of grinding step c) is obtainedprior to said grinding step by simultaneously contacting the calciumcarbonate-containing material provided in step a) with the at least onegrinding agent provided in step b).

According to another embodiment, the mixture of grinding step c) isobtained prior to said grinding step by simultaneously contacting thecalcium carbonate-containing material provided in step a) with a firstportion of the at least one grinding agent provided in step b), whereina second portion of the at least one grinding agent is added duringgrinding step c).

It has further been found by the inventors that grinding step c) ispreferably carried out at elevated temperatures. For the purposes of theprocess according to the present invention, a temperature ranging from65° C. to 200° C. is particularly suitable.

According to another embodiment, the temperature in step d) ranges from70° C. to 180° C., preferably from 75° C. to 160° C., and morepreferably from 80° C. to 150° C.

Process step c) involves the dry grinding of a mixture obtained bycontacting a calcium carbonate-containing material and at least onegrinding agent in at least one grinding unit to obtain a dry groundmineral filler.

In one embodiment, the dry ground mineral filler obtained after grindingstep c) has a weight median particle d₅₀ ranging from 0.5 to 100.0 μmand preferably from 1.0 to 30.0 μm.

Process Step d)

The dry ground mineral filler obtained in process step c) issubsequently subjected to classifying step d).

In said classifying step, the dry ground mineral filler of step c) isdivided into at least two fractions, i.e. into a coarse fraction and afine fraction.

A classifying step in general serves to divide a feed fraction having acertain particle size into a coarse fraction and a fine fraction eachhaving different particle sizes. Typically, the coarse fraction has ad₅₀ value being higher than that of the feed fraction, whereas the finefraction has a d₅₀ value being smaller than that of the feed fraction.For this purpose, screening devices as well as gravity-based devices,such as centrifuges or cyclones and any combination of theaforementioned devices may be used.

According to one embodiment, the dry ground mineral filler of step c) isclassified using a cyclone.

According to another embodiment, the fine mineral filler of step d) hasa weight median particle size d₅₀ ranging from 0.4 to 40.0 μm,preferably from 0.6 to 20.0 μm, and more preferably from 0.7 to 10.0 μm.

As already described above, the dry ground mineral filler of step c) isclassified in step d) to obtain a coarse fraction and a fine fraction,wherein the coarse fraction is removed or subjected to dry grinding stepc) and the fine fraction represents a fine mineral filler which mayrepresent the final product or may be used in one or more followingoptional process step.

To also use the coarse fraction obtained in classifying step d), saidcoarse material may be recycled. Therefore, in a preferred embodiment,the coarse fraction of step d) is subjected to dry grinding step c).

Process Step e)

The process according to the present invention further comprisesoptional drying step e). In said drying step, the fine mineral fillerobtained in classifying step d) is dried to obtain a dried mineralfiller.

In some cases, the total moisture content in the mixture of dry grindingstep c) may be very low. In these cases, for example, where the totalmoisture content in the mixture of step c) is less than or equal to 0.2wt.-%, preferably less than or equal to 0.1 wt.-%, and more preferablybetween 0.03 and 0.07 wt.-%, based on the total weight of said mixture,the process according to the present invention does not comprise anydrying step after classifying step d).

Therefore, according to one embodiment, the process for the preparationof a mineral filler product comprises the steps of:

-   -   a) providing a calcium carbonate-containing material;    -   b) providing at least one grinding agent;    -   c) dry grinding the calcium carbonate-containing material in a        mixture obtained by contacting:        -   i) the calcium carbonate-containing material provided in            step a), with        -   ii) the at least one grinding agent provided in step b) in            at least one grinding unit to obtain a dry ground mineral            filler; and    -   d) classifying the dry ground mineral filler of step c) to        obtain a coarse fraction and a fine fraction, wherein the coarse        fraction is removed or subjected to dry grinding step c) and the        fine fraction represents a fine mineral filler;    -   wherein the total moisture content in the mixture of step c) is        less than or equal to 10.0 wt.-%, based on the total weight of        said mixture;    -   the amount of the at least one grinding agent provided in        step b) ranges from 0.05 to 150 mg/m², based on the specific        surface area of the calcium carbonate-containing material as        measured by the BET nitrogen method;    -   the temperature in step c) ranges from 65° C. to 200° C.; and    -   the at least one grinding agent is selected from the group        consisting of styrene-maleic anhydride co-polymers and        derivatives of styrene-maleic anhydride co-polymers, and has a        monomer unit ratio (styrene units:maleic anhydride units, S:MA)        of from 1:2 to 15:1 and a molecular weight M_(w) of from 500 to        40,000 g/mol.

The mixture of step c) may also have a higher total moisture content butstill being less than or equal to 10.0 wt.-%, based on the total weightof said mixture. For example, the total moisture content of said mixturemay be less than or equal to 5.0 wt.-%, preferably less than or equal to2.0 wt.-%, and more preferably less than or equal to 1.0 wt.-%, based onthe total weight of said mixture. In these cases, a drying stepfollowing step c) may be mandatory in order to obtain a dried mineralfiller having a total moisture content of less than 1.0 wt.-%, based onthe total weight of said dried mineral filler.

According to another embodiment, the process for the preparation of amineral filler product thus comprises the steps of:

-   -   a) providing a calcium carbonate-containing material;    -   b) providing at least one grinding agent;    -   c) dry grinding the calcium carbonate-containing material in a        mixture obtained by contacting:        -   i) the calcium carbonate-containing material provided in            step a), with        -   ii) the at least one grinding agent provided in step b) in            at least one grinding unit to obtain a dry ground mineral            filler;    -   d) classifying the dry ground mineral filler of step c) to        obtain a coarse fraction and a fine fraction, wherein the coarse        fraction is removed or subjected to dry grinding step c) and the        fine fraction represents a fine mineral filler; and    -   e) drying the fine mineral filler of step d) to obtain a dried        mineral filler having a total moisture content of less than 1.0        wt.-%, based on the total weight of said dried mineral filler;    -   wherein the total moisture content in the mixture of step c) is        less than or equal to 10.0 wt.-%, based on the total weight of        said mixture;    -   the amount of the at least one grinding agent provided in        step b) ranges from 0.05 to 150 mg/m², based on the specific        surface area of the calcium carbonate-containing material as        measured by the BET nitrogen method;    -   the temperature in step c) ranges from 65° C. to 200° C.; and    -   the at least one grinding agent is selected from the group        consisting of styrene-maleic anhydride co-polymers and        derivatives of styrene-maleic anhydride co-polymers, and has a        monomer unit ratio (styrene units:maleic anhydride units, S:MA)        of from 1:2 to 15:1 and a molecular weight M_(w) of from 500 to        40,000 g/mol.

In particular, such a drying step may be mandatory in cases where the atleast one grinding agent provided in step b) is provided in form of anaqueous solution as has been described herein above. However, it has tobe noted that the provision of said grinding agent in form an aqueoussolution does not in any case require a mandatory drying step since thetotal amount of said at least one grinding agent is generally low.

Typically, the drying step according to the process of the presentinvention may be carried out by any drying method known to the skilledperson.

According to one embodiment, drying step e) is a spray drying step,preferably said spray drying step is carried out at a tower temperatureranging from 90° C. to 130° C. and preferably from 100° C. to 120° C.

By means of drying step e), a dried mineral filler is obtained having alow total moisture content which is less than or equal to 1.0 wt.-%,based on the total weight of said dried mineral filler.

According to another embodiment, the dried mineral filler of step e) hasa total moisture content of less than or equal to 0.5 wt.-% andpreferably less than or equal to 0.2 wt.-%, based on the total weight ofsaid dried mineral filler.

According to still another embodiment, the dried mineral filler of stepe) has a total moisture content of between 0.01 and 0.15 wt.-%,preferably between 0.02 and 0.10 wt.-%, and more preferably between 0.03and 0.07 wt.-%, based on the total weight of said dried mineral filler.

Optional Treatment Step

Independently from whether the process according to the presentinvention comprises an optional drying step or not, the process mayfurther comprise an optional step of treating (also referred to as“treatment step”) the fine mineral filler obtained in step d) and/or thedried mineral filler obtained in step e) with at least onehydrophobizing agent. By means of said treatment step, a treatment layeris formed on at least part of the surface of the obtained mineral fillerproduct.

Therefore, according to one embodiment, the process for the preparationof a mineral filler product comprises the steps of:

-   -   a) providing a calcium carbonate-containing material;    -   b) providing at least one grinding agent;    -   c) dry grinding the calcium carbonate-containing material in a        mixture obtained by contacting:        -   i) the calcium carbonate-containing material provided in            step a), with        -   ii) the at least one grinding agent provided in step b) in            at least one grinding unit to obtain a dry ground mineral            filler;    -   d) classifying the dry ground mineral filler of step c) to        obtain a coarse fraction and a fine fraction, wherein the coarse        fraction is removed or subjected to dry grinding step c) and the        fine fraction represents a fine mineral filler;    -   e) optionally drying the fine mineral filler of step d) to        obtain a dried mineral filler having a total moisture content of        less than 1.0 wt.-%, based on the total weight of said dried        mineral filler; and    -   f) optionally treating the fine mineral filler of step d) and/or        the dried mineral filler of step e) with a hydrophobizing agent        to obtain a surface-treated product having a treatment layer on        at least part of the surface of said product;    -   wherein the total moisture content in the mixture of step c) is        less than or equal to 10.0 wt.-%, based on the total weight of        said mixture;    -   the amount of the at least one grinding agent provided in        step b) ranges from 0.05 to 150 mg/m², based on the specific        surface area of the calcium carbonate-containing material as        measured by the BET nitrogen method;    -   the temperature in step c) ranges from 65° C. to 200° C.; and    -   the at least one grinding agent is selected from the group        consisting of styrene-maleic anhydride co-polymers and        derivatives of styrene-maleic anhydride co-polymers, and has a        monomer unit ratio (styrene units:maleic anhydride units, S:MA)        of from 1:2 to 15:1 and a molecular weight M_(w) of from 500 to        40,000 g/mol.

Said hydrophobizing agent used in the optional treatment step may be anyagent known to the skilled person which is capable to form a hydrophobictreatment layer on at least part of the surface of a mineral fillerproduct.

In one embodiment, the hydrophobizing agent is selected from the groupconsisting of fatty acids having from 6 to 24 chain carbon atoms,mono-substituted succinic anhydrides, alkyl phosphoric acid esters,polyhydrogensiloxane, polydimethylsiloxane, and mixtures thereof.

According to another embodiment, the hydrophobizing agent is a fattyacid having from 6 to 24 chain carbon atoms, preferably selected fromthe group consisting of stearic acid, behenic acid, palmitic acid,isostearic acid, montanic acid, capric acid, lauric acid, myristic acid,salts thereof, and mixtures thereof, and more preferably is stearic acidand/or a salt thereof

According to another embodiment, the hydrophobizing agent is an alkenylsuccinic anhydride.

According to still another embodiment, the hydrophobizing agent is analkyl phosphoric acid ester.

According to still another embodiment, the hydrophobizing agent isselected from polyhydrogensiloxane, polydimethylsiloxane, and mixturesthereof.

In some embodiments of the process according to the present invention,the temperature in the treatment step ranges from 70° C. to 140° C.,preferably from 75° C. to 130° C., and more preferably from 80° C. to125° C.

In some cases, the treatment step may be carried out directly at the endof the drying step. In one embodiment, drying step e) is thus carriedout in a drying unit comprising a drying chamber and the hydrophobizingagent of step f) is contacted with the dried mineral filler by directinjection of said agent into the drying chamber.

The Mineral Filler Product

As already described above, the moisture pick up susceptibility of amaterial refers to the amount of moisture absorbed on the surface ofsaid material and is expressed in mg moisture/g absorbed on a sampleupon exposure to a defined humid atmosphere.

In this respect, the fine mineral filler obtainable after classifyingstep d) and/or optional drying step e) may have a moisture pick upsusceptibility of less than or equal to 12.0 mg/g, preferably of lessthan or equal to 10.0 mg/g, and most preferably less than or equal to8.0 mg/g.

In another embodiment, the mineral filler product obtainable by theoptional treatment step may have a moisture pick up susceptibility ofless than or equal to 3.0 mg/g, preferably of less than or equal to 2.5mg/g, and most preferably less than or equal to 2.0 mg/g.

In another embodiment, the mineral filler product obtainable by theoptional treatment step has a moisture pick up susceptibility of lessthan or equal to 0.9 mg/g, preferably less than or equal to 0.8 mg/g,more preferably less than or equal to 0.7 mg/g, and most preferably lessthan or equal to 0.6 mg/g.

In another embodiment, the mineral filler product obtainable by theoptional treatment step has a moisture pick up susceptibility of from0.1 to 0.9 mg/g, preferably from 0.2 to 0.8 mg/g, and most preferablyfrom 0.2 to 0.6 mg/g.

In some particular cases as, for example in case of high specificsurface areas of the mineral filler product, the moisture pick upsusceptibility is suitably defined based on the specific surface area ofsaid product (referred to as the normalized moisture pick upsusceptibility).

According to one embodiment, the mineral filler product obtainable bythe optional treatment step has a normalized moisture pick upsusceptibility of less than or equal to 0.18 mg/m², preferably less thanor equal to 0.17 mg/m², more preferably less than or equal to 0.16mg/m², and most preferably less than or equal to 0.15 mg/m², based onthe specific surface area of said product as measured by the BETnitrogen method.

According to one embodiment, the mineral filler product obtainable bythe optional treatment step has a normalized moisture pick upsusceptibility of from 0.10 to 0.18 mg/m², preferably from 0.11 to 0.17mg/m², and most preferably from 0.12 to 0.16 mg/m², based on thespecific surface area of said product as measured by the BET nitrogenmethod.

According to another embodiment, the mineral filler product obtainableafter classifying step d) and/or optional drying step e) has a specificsurface area ranging from 0.1 to 20.0 m²/g and more preferably from 3.0to 14.0 m²/g as measured by the BET nitrogen method.

According to still another embodiment, also the mineral filler productobtainable by the optional treatment step has a specific surface arearanging from 0.1 to 20.0 m²/g and more preferably from 3.0 to 14.0 m²/gas measured by the BET nitrogen method.

By means of the process according to the present invention, a low totalvolatiles content and, in particular, a high volatile onset temperaturemay be achieved.

In one embodiment, the mineral filler product according to the presentinvention may have a volatile onset temperature of at least or equal to200° C., preferably at least or equal to 230° C., and more preferably atleast or equal to 250° C. These values likewise refer to the finemineral filler of step d) of the process according to the presentinvention, to the dried mineral filler of drying step e) and to theproduct obtainable by the optional treatment step.

The inventive mineral filler product may be used in a polymercomposition, in paper making, paper coatings, agricultural applications,paints, adhesives, sealants, construction applications, and/or cosmeticapplications, preferably said mineral filler product is used in apolymer composition.

As the mineral filler product has a low moisture pick up susceptibility,it may advantageously be used in paper coatings in order to adjust theprinting properties of a coated paper. Furthermore, the mineral fillerproduct may also be used in exterior paints and bathroom paints whichmay lead to a reduction in mildew growth on surfaces being treated withsuch paints.

A number of the aforementioned applications (e.g., for coatings orpaints) involve the preparation of an aqueous slurry comprising themineral filler product obtainable by the process according to thepresent invention. Such aqueous slurries may be easily prepared from theinventive mineral filler product by the addition of water to obtainslurries having a solids content of, for example, from 10.0 to 85.0wt-%, based on the total weight of said slurry.

The use of the mineral filler product according to the present inventionas a filler material in polymer applications may also be of particularadvantage. For example, said filler may be used in thermoplasticpolymers, such as polyvinyl chloride, polyolefins, and polystyrene whichmay allow an increased filler load as compared to conventional calciumcarbonate fillers.

Moreover, the mineral filler product may also be used in polymercoatings which may be applied on the surface of polymer articles, suchas foils, in order to increase the hydrophobicity (e.g., reflected by anincreased contact angle measured against water) of said surface.

According to one embodiment, the mineral filler product is used in apolymer composition, wherein said polymer composition comprises:

-   -   a) at least one polymeric resin; and    -   b) from 0.1 to 90.0 wt.-%, preferably from 1.0 to 85.0 wt.-%,        and more preferably from 2.0 to 45.0 wt.-%, based on the total        weight of said polymer composition, of the mineral filler        product obtainable by the process according to the present        invention.

According to another embodiment, said at least one polymeric resin is athermoplastic resin and preferably is a polyolefin, polyvinylchloride,or polystyrene.

According to another embodiment, said at least one polymeric resin is apolyolefin and preferably polyethylene or polypropylene.

According to still another embodiment, said at least one polymeric resinis polyvinylchloride.

According to still another embodiment, said at least one polymeric resinis polystyrene.

The polymer composition of the present invention may be used in a numberof processes including the manufacture of blown films, sheets, or pipeprofiles, in processes such as extrusion of pipes, profiles, cables,fibres or the like, and in compression molding, injection molding,thermoforming, blow molding, rotational molding, etc.

In this respect, said polymer composition may be directly used in themanufacture of polymer articles. Therefore, in one embodiment of thepresent invention, the polymer composition comprises the mineral fillerproduct in an amount of from 1 to 50 wt.-%, preferably of from 5 to 45wt.-% and most preferably from 10 to 40 wt.-%, based on the total weightof the polymer composition.

In an alternative embodiment, the polymer composition may be used as amasterbatch.

The term “masterbatch” refers to a composition having a concentration ofthe mineral filler product that is higher than the concentration in thepolymer composition used for preparing the final application product.That is to say, the masterbatch is further diluted such as to obtain apolymer composition which is suitable for preparing the finalapplication product.

For example, a polymer composition according to the present inventionsuitable to be used as a masterbatch comprises the mineral fillerproduct in an amount of from 50 to 95 wt.-%, preferably from 60 to 95wt.-%, and more preferably from 70 to 95 wt.-%, based on the totalweight of the polymer composition.

EXAMPLES

The scope and interest of the invention may be better understood onbasis of the following examples which are intended to illustrateembodiments of the present invention. However, they are not to beconstrued to limit the scope of the claims in any manner whatsoever.

Weight Average Molecular Weight M_(w)

The weight average molecular weight M_(w) as used herein may bedetermined using GPC (SEC) as follows:

A sample corresponding to 90 mg of dry polymer is introduced into a 10ml flask and at least 1 ml of 5 M aqueous NaOH is added until the pHvalue does change by not more than 0.3 pH units within 48 hours. Mobilephase with an additional 0.04 wt.-% of dimethylformamide is added untila total mass of 10 g is reached. The composition of the mobile phase atpH 9 is as follows: 0.05 M NaHCO₃, 0.1 M NaNO₃, 0.02 M triethanolamine,0.03 wt.-% of NaN₃.

The SEC equipment is consisting of an isocratic Waters™ 515 type pump,the flow rate of which is set to 0.8 ml/min, a Waters™ 717+samplechanger, a kiln containing a precolumn type Guard Column UltrahydrogelWaters™ which is 6 cm in length and has an internal diameter of 40 mm,followed by a linear column type Ultrahydrogel Waters™ which is 30 cm inlength and has an internal diameter of 7.8 mm.

Detection is accomplished by means of a Waters™ 410 differentialrefractometer. The kiln is heated to a temperature of 60° C. and therefractometer is heated to a temperature of 45° C.

The SEC is calibrated with a series of sodium polyacrylate standardssupplied by Polymer Standard Service having maximum molecular weight ofbetween 2,000 and 1·10⁶ g/mol and a polydispersity index of between 1.4and 1.7 and further with a sodium polyacrylate of average weightmolecular weight of 5,600 g/mol and a polydispersity index equal to 2.4.

The calibration graph is of the linear type and takes account of thecorrection obtained using the flow rate marker (dimethylformamide).

Measurement of Volatiles

For the purpose of the present application, the “total volatiles”associated with mineral fillers and evolved over a temperature range of25° C. to 350° C. is characterized by % of mass loss of a mineral fillersample over a temperature range as read on a thermogravimetric (TGA)curve.

TGA analytical methods provide information regarding losses of mass andvolatile onset temperatures with great accuracy. The methods arewell-known to the skilled person and described in, for example,“Principles of Instrumental analysis”, 5^(th) edition, Skoog HollerNieman, 1998, chapter 31, pp. 798-800. In the present invention,thermogravimetric analysis (TGA) is performed using a Mettler Toledo TGA851 based on a sample of 500±50 mg and scanning temperatures of from 25°C. to 350° C. at a rate of 20° C./min under an air flow of 70 ml/min.

The “volatile onset temperature” can be determined as follows byanalysis of the TGA curve: The first derivative of the TGA curve isobtained and the inflection points thereon between 150° C. and 350° C.are identified. Among these inflection points having a tangential slopevalue of greater than 45° relative to a horizontal line, the one havingthe lowest associated temperature above 200° C. is identified. Thetemperature associated with this lowest inflection point of the firstderivative curve is the “volatile onset temperature”.

Particle Size Distribution

For the purpose of the present application, particle sizes being lowerthan 100 μm, the weight median particle size d₅₀ and furthergranulometric characteristics are determined based on measurements madeby using a Sedigraph™ 5100 instrument of Micromeritics InstrumentCorporation. The method and the instrument are known to the skilledperson and are commonly used to determine the particle size of fillersand pigments. The measurement is carried out in an aqueous solution of0.1 wt.-% Na₄P₂O₇. The samples are dispersed using a high speed stirrerand supersonics. In case of surface-treated products, additional 0.5 gof a surfactant (Photo-Flo 200® from Kodak) were added to 50 ml of thesolution of 0.1 wt.-% Na₄P₂O₇ before dispersing the treated carbonatesample.

In case of particle sizes being greater than 100 μm, fractional sievingis used to determine granulometric characteristics.

BET Specific Surface Area of a Material

Throughout the present document, the specific surface area (expressed inm²/g) of a mineral filler is determined using the BET method (usingnitrogen as adsorbing gas), which is well known to the skilled person(ISO 9277:1995). The total surface area (in m²) of the mineral fillercan be obtained by multiplication of the specific surface area (in m²/g)and the mass (in g) of the mineral filler.

Moisture Pick Up Susceptibility

The moisture pick up susceptibility of a material as referred to hereinis determined in mg moisture/g after exposure to an atmosphere of 10 and85% relative humidity, respectively, for 2.5 hours at a temperature of+23° C. (±2° C.). For this purpose, the sample is first kept at anatmosphere of 10% relative humidity for 2.5 hours, then the atmosphereis changed to 85% relative humidity at which the sample is kept foranother 2.5 hours. The weight increase between 10 and 85% relativehumidity is then used to calculate the moisture pick-up in mg moisture/gof sample.

The moisture pick up susceptibility in mg/g divided by the specificsurface area in m² (BET method) corresponds to the “normalized moisturepick up susceptibility” expressed in mg/m² of sample.

Total Moisture Content

The total moisture content as used herein is measured according to theKarl Fischer coulometric titration method, desorbing the moisture in anoven at 220° C. for 10 min and passing it continuously into a KFcoulometer (Mettler Toledo coulometric KF Titrator C30, combined withMettler oven DO 0337) using dry nitrogen at 100 ml/min for 10 min. Acalibration curve using water has to be recorded and a blank of 10 minnitrogen flow without a sample has to be taken into account.

Materials

-   -   Grinding agent A        MPG=monopropylene glycol.    -   Grinding agent B        Cray Valley SMA 1000HNa=aqueous solution of hydrolyzed        styrene-maleic anhydride co-polymer, 100% sodium neutralized,        commercially available from Cray Valley LLC, USA; approx.        molecular weight M_(w)=5,000 g/mol; monomer unit ratio        (S:MA)=1:1; 40.4 wt.-% grinding agent content; pH=8.5.    -   Grinding agent C        Cray Valley SMA 1000=powdered styrene-maleic anhydride        co-polymer, commercially available from Cray Valley LLC, USA;        approx. molecular weight M_(w)=5,000 g/mol; monomer unit ratio        (S:MA)=1:1.    -   Grinding agent D        Cray Valley SMA 3000HNa=aqueous solution of hydrolyzed        styrene-maleic anhydride co-polymer, 100% sodium neutralized,        commercially available from Cray Valley LLC, USA; approx.        molecular weight M_(w)=9,500 g/mol; monomer unit ratio        (S:MA)=3:1; 24.4 wt.-% grinding agent content; pH=8.6.    -   Grinding agent E        Cray Valley SMA EF-30=powdered styrene-maleic anhydride        co-polymer, commercially available from Cray Valley LLC, USA;        approx. molecular weight M_(w)=9.500 g/mol; monomer unit ratio        (S:MA)=3:1.    -   Grinding agent F        Cray Valley SMA EF-40=solution in acetone prepared from        styrene-maleic anhydride co-polymer, commercially available from        Cray Valley LLC, USA; approx. molecular weight M_(w)=11,000        g/mol; monomer unit ratio (S:MA)=4:1; 33.0 wt.-% grinding agent        content.    -   Grinding agent G        Cray Valley SMA 17352=partially esterified styrene-maleic        anhydride co-polymer in powdered form, commercially available        from Cray Valley LLC, USA; approx. molecular weight M_(w)=7,000        g/mol; acid value: 270 mg KOH/g.    -   Grinding agent H        Cray Valley SMA 1440=partially esterified styrene-maleic        anhydride co-polymer in powdered form, commercially available        from Cray Valley LLC, USA; approx. molecular weight M_(w)=7,000        g/mol; acid value: 185 mg KOH/g.        General Procedure

Italian marble having an average diameter of approx. 5 cm was crushedusing a hammer mill. The size distribution of the crushed material wasdetermined by sieving and is given in Table 1 herein below.

The crushed material was contacted with one of the grinding agentssummarized above immediately before grinding and mixed in a concretemixer for at least 10 min.

The obtained material was then transferred into a ball mill (Hosokawa™Ball Mill S.O. 80/32) using 100 kg of cylindrically shaped iron grindingballs, having an average diameter of 16 mm in order to obtain a groundmaterial having a weight median particle size d₅₀ of less than or equalto 1.0 μm.

The outlet of the grinding chamber was equipped with an opening of 20×5mm discharging to an Alpine Turboplex™ 100 ATP classifier. Theclassifier was adjusted in order to recover the fine fraction having adesired weight median particle size d₅₀. The remaining coarse materialhaving a weight median particle size d₅₀ being higher than said desiredvalue is sent back to the mill feed.

The dry grinding was performed in a continuous fashion, wherein approx.15 kg of material were constantly present in the system. Thus, the millfeed was continuously fed with a quantity of crushed material and/orcoarse fraction material resulting from the classifying step materialwhich was equal to the quantity of the fine fraction leaving the system.

The system was operated until constant amounts of material having asuitable quality could be recovered by monitoring the grinding capacityand the grinding energy. The grinding chamber is heated to a constanttemperature of 80° C.

TABLE 1 Particle size distribution of crushed marble. Particle sizefraction wt.-% >1 mm 28.3 0.5 to 1 mm 8.7 200 to 500 μm 18.3 100 to 200μm 18.1 50 to 100 μm 11.6 <50 μm 15.0

TABLE 2 Process throughput and particle sizes after grinding. Particlesize Grinding Grinding distribution Example agent agent Throughput d₁₀d₅₀ d₉₈ no. type [ppm] [kg/h] [μm] [μm] [μm] 1 A 1′500 1.6 0.34 1.02 3.42 B 1′500 2.3 0.30 0.92 5.3 3 C 1′500 2.6 0.31 0.93 3.6 4 D 1′500 2.50.32 0.92 3.1 5 E 1′500 2.2 0.34 1.00 3.4 6 F 1′500 2.7 0.35 1.03 3.1 7B 7′500 3.2 0.34 1.11 3.5 8 G 1′500 2.9 0.31 0.93 2.14 9 H 1′500 3.20.31 0.95 2.10

TABLE 3 Volatile onset temperatures. Example Grinding agent Grindingagent Final product no. type [ppm] Volatile onset [° C.] 1 A 1′500 178 2B 1′500 336 3 C 1′500 337 4 D 1′500 341 5 E 1′500 383 6 F 1′500 380 7 B7′500 320 8 G 1′500 359 9 H 1′500 381

These examples illustrate the improved grinding capacities (i.e. anincreased throughput) in a process according to the present invention ascompared to a process carried out in the absence of grinding agent orusing a conventional grinding agent.

The invention claimed is:
 1. A process for the preparation of a mineralfiller product, the process comprising the steps of: a) providing acalcium carbonate-containing material; b) providing at least onegrinding agent; c) dry grinding the calcium carbonate-containingmaterial in a mixture obtained by contacting: i) the calciumcarbonate-containing material provided in step a), with ii) the at leastone grinding agent provided in step b), in at least one grinding unit toobtain a dry ground mineral filler; d) classifying the dry groundmineral filler of step c) to obtain a coarse fraction and a finefraction, wherein the coarse fraction is removed or subjected to drygrinding step c) and the fine fraction represents a fine mineral filler;and e) optionally drying the fine mineral filler of step d) to obtain adried mineral filler having a total moisture content of less than 1.0wt.-%, based on the total weight of said dried mineral filler; whereinthe total moisture content in the mixture of step c) is less than orequal to 10.0 wt.-%, based on the total weight of said mixture; theamount of the at least one grinding agent provided in step b) rangesfrom 0.05 to 150 mg/m², based on the specific surface area of thecalcium carbonate-containing material as measured by the BET nitrogenmethod; the temperature in step c) ranges from 65° C. to 200° C.; andthe at least one grinding agent is selected from the group consisting ofstyrene-maleic anhydride co-polymers and derivatives of styrene-maleicanhydride co-polymers, and has a monomer unit ratio (styrene units :maleic anhydride units, S:MA) of from 1:2 to 15:1 and a molecular weightM_(W), of from 500 to 40,000 g/mol.
 2. The process according to claim 1,wherein the calcium carbonate-containing material provided in step a) isfrom a natural calcium carbonate source selected from the groupconsisting of marble, limestone, chalk, dolomite, and any mixturethereof.
 3. The process according to claim 1, wherein the amount of saidat least one grinding agent provided in step b) ranges from 0.1 to 100.0mg/m², based on the specific surface area of the calciumcarbonate-containing material as measured by the BET nitrogen method. 4.The process according to claim 1, wherein the amount of said at leastone grinding agent provided in step b) ranges from 0.2 to 75.0 mg/m²,based on the specific surface area of the calcium carbonate-containingmaterial as measured by the BET nitrogen method.
 5. The processaccording to claim 1, wherein the amount of said at least one grindingagent provided in step b) ranges from 0.2 to 50.0 mg/m², based on thespecific surface area of the calcium carbonate-containing material asmeasured by the BET nitrogen method.
 6. The process according to claim1, wherein the at least one grinding agent provided in step b) has amonomer unit ratio (S:MA) of from 1:1 to 5:1.
 7. The process accordingto claim 1, wherein the at least one grinding agent provided in step b)has a monomer unit ratio (S:MA) of from 1:1 to 4:1.
 8. The processaccording to claim 1, wherein the at least one grinding agent providedin step b) has a monomer unit ratio (S:MA) of from 1:1 to 3:1.
 9. Theprocess according to claim 1, wherein the at least one grinding agentprovided in step b) has a molecular weight M_(W), of from 2,000 to30,000 g/mol.
 10. The process according to claim 1, wherein the at leastone grinding agent provided in step b) has a molecular weight M_(W), offrom 3,000 to 25,000 g/mol.
 11. The process according to claim 1,wherein the at least one grinding agent provided in step b) is partiallyor fully neutralized with a cation selected from the group consisting oflithium, sodium, potassium, calcium, magnesium, ammonium, iminium, andany mixture thereof.
 12. The process according to claim 1, wherein thetotal moisture content in the mixture of step c) is less than or equalto 5.0 wt.-%, based on the total weight of said mixture.
 13. The processaccording to claim 1, wherein the total moisture content in the mixtureof step c) is less than or equal to 2.0 wt.-%, based on the total weightof said mixture.
 14. The process according to claim 1, wherein the totalmoisture content in the mixture of step c) is less than or equal to 1.0wt.-%, based on the total weight of said mixture.
 15. The processaccording to claim 1, wherein the temperature in step c) ranges from 70°C. to 180° C.
 16. The process according to claim 1, wherein thetemperature in step c) ranges from 75° C. to 160° C.
 17. The processaccording to claim 1, wherein the temperature in step c) ranges from 80°C. to 150° C.
 18. The process according to claim 1, wherein the finemineral filler of step d) has a weight median particle size d₅₀ rangingfrom 0.4 to 40.0 μm.
 19. The process according to claim 1, wherein thefine mineral filler of step d) has a weight median particle size d₅₀ranging from 0.6 to 20.0 μm.
 20. The process according to claim 1,wherein the fine mineral filler of step d) has a weight median particlesize d₅₀ ranging from 0.7 to 10.0 μm.
 21. The process according to claim1, wherein the process further comprises a step of treating the finemineral filler of step d) and/or the dried mineral filler of step e)with a hydrophobizing agent to obtain a surface-treated product having atreatment layer on at least part of the surface of the product.